The invention relates to cementitious compositions and products made from such compositions. More particularly, the invention relates to substantially clay-free compositions comprising a hydraulic cement, water, a water-soluble polymer and a cross-linking agent for said polymer. It is to be understood that the compositions according to this invention are substantially clay-free.
By the term "reactive water-soluble polymer" in this specification is meant any water-soluble or water dispersible polymer or mixture of such polymers which can be reacted with an appropriate cross-linking agent to cause the polymer to become insoluble, or substantially so, in products made from the cementitious compositions of this invention.
By the term "hydraulic cement" in this specification, there is meant any material which sets and hardens by the addition of water, that is in the presence of water. The hydraulic cement may, for example, be a silicate cement such as Portland cement or it may be an aluminate cement. The term includes mixtures of two or more different hydraulic cements.
In making cementitious products, it is desirable that the resultant product should be of high strength and especially high flexural strength. This is particularly important when the products are to be used as building products, for example roofing slates, and for use in such applications it is desirable that the products should not only have a flexural strength of at least 15 MPa and advantageously 40 MPa, but also good durability, i.e. good resistance to:
(a) variations in climatic conditions particularly freeze-thaw conditions and cycles of alternate rain and sunshine; PA1 (b) ultra-violet attack; PA1 (c) acid rain; and, PA1 (d) abrasion of surfaces by the elements PA1 (a) at least one hydraulic cement; PA1 (b) at least one reactive water-soluble polymer which is capable of providing a viscous solution in water at low addition levels as hereinbefore defined; PA1 (c) water in an amount of from 10 to 25 parts by weight of water per 100 parts by weight of the cement; and PA1 (d) a water soluble cross-linking agent capable of effecting chemical cross-links between molecules of the said polymer in the presence of the cement and water. PA1 (a) labile chlorine reagents PA1 (b) sulphones PA1 (c) epoxides PA1 (a) a cellulose ether plus a diepoxide; PA1 (b) a cellulose ether plus a sulphone; PA1 (c) a cellulose ether plus a compound containing labile chlorine; PA1 (d) a cellulose ether plus ethylene imine; PA1 (e) a carboxycellulose ether with polyvalent cation; PA1 (f) polyacrylamide, or a derivative thereof or a copolymer of acrylamide plus a dialdehyde; PA1 (g) polyvinylalcohol or partially hydrolised polyvinlacetate plus an inorganic acid; PA1 (h) gelatin plus formaldehyde; PA1 (i) polyacrylic acid or polyacrylic acid salt plus diexpoxide; PA1 (j) a cellulose ether plus an acrylamide monomer, and a free radical initiator or heat; PA1 (k) an allyl substituted cellulose ether plus a free radical initiator or heat.
such that the strength of the building product is maintained satisfactorily throughout its life.
Cementitious products produced from an hydraulic cement paste consisting of hydraulic cement and water only generally have low strength, especially low flexural strength, and poor durability. For example, a product formed from a cementitious composition which comprises an ordinary hydraulic cement with a typical spread of particle size range and an amount of water which is conventionally used in such compositions may have a flexural strength as low as 5 to 10 MPa. Moreover unless substantial amounts of aggregate (i.e. sand or crushed rock or the like) are incorporated into such cementitious products they will not normally be durable in natural weathering conditions.